6.13-stable review patch. If anyone has any objections, please let me know.
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From: Tianchen Ding dtcccc@linux.alibaba.com
[ Upstream commit 5d808c78d97251af1d3a3e4f253e7d6c39fd871e ]
We met a SCHED_WARN in set_next_buddy(): __warn_printk set_next_buddy yield_to_task_fair yield_to kvm_vcpu_yield_to [kvm] ...
After a short dig, we found the rq_lock held by yield_to() may not be exactly the rq that the target task belongs to. There is a race window against try_to_wake_up().
CPU0 target_task
blocking on CPU1 lock rq0 & rq1 double check task_rq == p_rq, ok woken to CPU2 (lock task_pi & rq2) task_rq = rq2 yield_to_task_fair (w/o lock rq2)
In this race window, yield_to() is operating the task w/o the correct lock. Fix this by taking task pi_lock first.
Fixes: d95f41220065 ("sched: Add yield_to(task, preempt) functionality") Signed-off-by: Tianchen Ding dtcccc@linux.alibaba.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Link: https://lkml.kernel.org/r/20241231055020.6521-1-dtcccc@linux.alibaba.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/sched/syscalls.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/sched/syscalls.c b/kernel/sched/syscalls.c index ff0e5ab4e37cb..943406c4ee865 100644 --- a/kernel/sched/syscalls.c +++ b/kernel/sched/syscalls.c @@ -1433,7 +1433,7 @@ int __sched yield_to(struct task_struct *p, bool preempt) struct rq *rq, *p_rq; int yielded = 0;
- scoped_guard (irqsave) { + scoped_guard (raw_spinlock_irqsave, &p->pi_lock) { rq = this_rq();
again: